1. Field of the Invention
The invention pertains to the field of variable cam timing systems. More particularly, the invention pertains to a remote control valve of a variable cam timing system with lock pin control.
2. Description of Related Art
Locking pins are commonly added to phasers to lock the position of the rotor relative to the housing. Some of examples of phasers with locking pins are U.S. Pat. No. 6,477,999, U.S. Pat. No. 6,481,402, U.S. Pat. No. 6,644,258, U.S. Pat. No. 6,668,778, U.S. Pat. No. 6,766,777, and U.S. Pat. No. 6,772,721.
U.S. Pat. No. 6,477,999 discloses a passage in the sprocket that extends parallel to and spaced from a longitudinal axis of rotation of the camshaft. A pin is slidable within the passage and is resiliently urged by a spring. A vane of the phaser carries a plate with a pocket for receiving an end of the pin. If sufficient oil pressure is provided, the oil pressure keeps the end of the pin from engaging the pocket in the vane, if not, the pin engages the pocket prohibiting movement of the vane. The pocket is in fluid communication with the oil used in the variable cam timing system.
U.S. Pat. No. 6,481,402 discloses a variable cam timing system in which the rotor and the housing are locked relative to each other by a pin when the spool is in the null position. Pressurized fluid from a source provides fluid to a lock pin passage off of the fluid line to either the advance chamber or the retard chamber.
U.S. Pat. No. 6,644,258 discloses a pin in the housing that locks the housing relative to the rotor. The oil pressure required to unlock the locking pin is higher than the pressure required to the hold the pin in the unlocked position.
U.S. Pat. No. 6,668,778 discloses a locking pin in hydraulic communication with a control circuit of a differential pressure control system (DPCS) of a variable cam timing system. When the control pressure is less than 50% duty cycle, a control signal commands the pin to engage and the VCT to move toward the mechanical stop. When the control pressure of the circuit is greater than 50% duty cycle, the locking pin disengages and the vane moves away from the mechanical stop.
U.S. Pat. No. 6,766,777 discloses a variable cam timing system in which a source oil passage provides oil to a spool valve and a locking pin. The locking pins is fed directly from the source. When the oil pump is on, the locking pin is unlocked. The spool position has no bearing on whether the locking pin is locked or unlocked.
U.S. Pat. No. 6,772,721 discloses a variable cam timing system having a rotor with two sets of vanes including vanes with a pair of shoulders. The shoulders position and block the passage way to a locking pin. In the advanced, retard, and null positions, the locking pin is unlocked. In the full advance position the locking pin is locked. The locking pin is pressurized when the spool is commanded to move away from its default position.
U.S. Pat. No. 6,814,038 discloses a variable cam timing system that utilizes the same spool that controls the VCT mechanism to actively control the locking pin. The positions of the spool's multiple lands directly influence whether source oil is supplied to both the locking pin and either the retard or advance chamber of the phaser.
FIGS. 5a–5c show a prior art cam torque actuated (CTA) phaser. In cam torque actuated phasers, torque reversals in the camshaft caused by the forces of opening and closing the valves move the vane 6. The control valve 4 in the CTA system allows the vanes 6 in the phaser to move by permitting fluid flow from the advance chamber 8 to the retard chamber 10 or vice versa, depending on the desired direction of movement. Positive cam torsionals are used to retard the phaser and negative cam torsionals are used to advance the phaser. During operation of the cam torque actuated phaser, the spool valve 4 pressurizes both the advance 8 and retard chambers 10 simultaneously and circulates oil to and from the spool valve 4 to the chambers 8, 10. Since, both chambers 8, 10 are pressurized simultaneously in the cam torque actuated phaser, a locking pin could never be added directly off of the chambers, since the pressure is never reduced to zero.
More specifically, in the null position, as shown in FIG. 5a, spool lands 9a, 9b block lines 12 and 13, and vane 6 is locked into position. Additional fluid is provided to the phaser to makeup for losses due to leakage. In this position, the locking pin in a bore 52 is in an unlocked position. Fluid is supplied to the locking pin from a source by line 50 and 54. The pressure of the fluid from source is greater than the force exerted by biasing spring 23 on locking pin 24. The locking pin 24 is prevented from venting by spool land 9b. Furthermore, in some engines the cam torque energy dissipates at high speeds, and the CTA VCT is not able to move without cam torque energy, because by the nature of the CTA hydraulic circuit, equal source pressure is applied to both sides of the vane, such that the VCT does not move.
To retard the phaser, as shown in FIG. 5b, hydraulic fluid from the supply enters line 18 and moves through check valve 19 to the spool valve 4. The spool valve 4 is internally mounted and comprises a sleeve 17 for receiving a spool 9 with lands 9a, 9b, and 9c and a biasing spring 5. A variable force solenoid or actuator 3, which is controlled by an ECU 2, moves the spool 9 within the sleeve 17. The spool is moved to the left by spring 5, and spool land 9b blocks line 13 and partially opens exhaust line 21, while spool land 9c blocks line 54 and source fluid to line 50 and locking pin 24. Without the pressure of source fluid, biasing spring 23 forces the locking pin 24 to a locked position. All or any fluid present in the bore 52 with the locking pin is vented to line 21. Lines 12 and 16 are open. From the spool 9, fluid enters line 16 through open check valve 15 into line 13 and to the retard chamber 10. At the same time fluid is exiting the advance chamber 8 through line 12 and fluid moves through the spool between lands 9a and 9b and back into line 16 where it feeds into line 13 supplying fluid to the retard chamber 10.
To advance the phaser, as shown in FIG. 5c, the spool is moved by the VFS 3 to the right, so that spool land 9a and 9b do not block line 13, line 16, or any exhaust lines and spool land 9a blocks the exit of fluid from line 12. Fluid from the retard chamber 10 exits the chamber through line 13, which routes the fluid through the spool 9 between lands 9a and 9b. The fluid then enters line 16 and travels through open check valve 14 into line 12 and the advance chamber 8. Additional fluid is supplied by the supply through line 18 and check valve 19 to the spool valve 4. In this position, the locking pin 24 is in an unlocked position. Source fluid and pressure is provided to the bore 52 of the locking pin 24 by lines 50 and 54. The pressure of the fluid from source is greater than the force exerted by biasing spring 23 on locking pin 24. The locking pin 24 is prevented from venting by spool land 9b. 